// When the extension is installed or upgraded ...
chrome.runtime.onInstalled.addListener(function() {

 // Replace all rules ...
 chrome.declarativeContent.onPageChanged.removeRules(undefined, function() {
   // With a new rule ...
    chrome.declarativeContent.onPageChanged.addRules([
      {
        // That fires when a page's URL contains a 'g' ...
        conditions: [
          new chrome.declarativeContent.PageStateMatcher({
            pageUrl: { urlMatches: '.*youtube.com/watch.*'},
    })
      ],
       // And shows the extension's page action.
       actions: [ new chrome.declarativeContent.ShowPageAction() ]
     }
   ]);
  });
  
});
